tast: Use ~/chromiumos instead of ~/trunk for src files.

At present, tast uses ~/trunk to look at some src files when creating
the config to run the tests. This was due to legacy usages and is now
deprecated. Update to use the ~/chromiumos instead to look at sources.

BUG=b:216867892
TEST=Ran `./fast_build.sh -T` to make sure all tests pass. Also, ran `tast -verbose run 127.0.0.1:9222 diagnostics.Input` to make sure that passes.

Change-Id: Icf8e93389730b2557ce3e6a7f1976195f066a7e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/tast/+/3449714
Commit-Queue: Srinivas Hegde <srinivashegde@google.com>
Tested-by: Srinivas Hegde <srinivashegde@google.com>
Reviewed-by: Seewai Fu <seewaifu@google.com>
diff --git a/fast_build.sh b/fast_build.sh
index ed99552..65f4c24 100755
--- a/fast_build.sh
+++ b/fast_build.sh
@@ -15,9 +15,9 @@
 
 # Go workspaces containing the Tast source.
 readonly SRCDIRS=(
-  "${HOME}/trunk/src/platform/tast"
-  "${HOME}/trunk/src/platform/tast-tests"
-  "${HOME}/trunk/src/platform/tast-tests-private"
+  "${HOME}/chromiumos/src/platform/tast"
+  "${HOME}/chromiumos/src/platform/tast-tests"
+  "${HOME}/chromiumos/src/platform/tast-tests-private"
 )
 
 # Package to build to produce tast executables.
diff --git a/src/chromiumos/tast/cmd/tast/paths.go b/src/chromiumos/tast/cmd/tast/paths.go
index ff78620..77e5577 100644
--- a/src/chromiumos/tast/cmd/tast/paths.go
+++ b/src/chromiumos/tast/cmd/tast/paths.go
@@ -9,10 +9,15 @@
 	"path/filepath"
 )
 
-const tastDir = "/tmp/tast" // base directory where Tast writes files
+const (
+	// base directory where Tast writes files
+	tastDir = "/tmp/tast"
+	// Path to the src files
+	srcDir = "chromiumos"
+)
 
 // trunkDir returns the path to the Chrome OS checkout (within a chroot).
 func trunkDir() string {
 	// TODO(derat): Should probably check that we're actually in the chroot first.
-	return filepath.Join(os.Getenv("HOME"), "trunk")
+	return filepath.Join(os.Getenv("HOME"), srcDir)
 }